Conventionally, CDMA (Code Division Multiple Access) and WCDMA (Wideband CDMA) are proposed as a technique for transmitting multiple signals efficiently.
In CDMA, a transmitting side superimposes different spreading codes on multiple signals and adds them, and transmits a result. A receiving side obtains a correlation between each allocated spreading code and a received signal as being shifted to use a high correlation point as a synchronizing point, and superimposes the spreading codes based on the synchronizing point to restore a signal addressing to the receiving side itself.
In WCDMA that is the most simplest and is currently used in Japan, the transmitting side has two channels, which superimpose different spreading codes on multiple signals and adds them, allocates each of outputs of these systems to an I-channel and a Q-channel, which are different in phase by 90°, and transmits them. Then, these multiple signals are generally synchronized with one another.
Moreover, the document shown below describes the technique of asynchronous user CDMA, and asserts that an amount of interference noise in asynchronous user CDMA is small as compared with synchronous user CDMA.
[Non-patent document 1] M. B. Pursely, Performance Evaluation for Phased-Coded Spread-Spectrum Multiple-Access Communication Part 1: System Analysis, IEEE Trans-Communications, Vol. 25 (1977), pp. 795-799
However, a more excellent technique has been strongly desired that transmits multiple synchronized signals efficiently, facilitates the separation thereof at a receiving side to reduce a bit error rate.
It is an object of the present invention is to provide a transmitter apparatus, which is suitable for transmitting multiple synchronized signals in such a way to be efficiently separated from one another at a receiving side, receiver apparatus, transmission method, and a program that causes a computer to execute these.